The present invention is directed to an inter-technology roaming proxy that translates and routes requests and responses between two networks having different protocols.
Conventional wireless telecommunications networks include Base Stations, Mobile Switching Centers (MSCs) equipped with Visitor Location Registers (VLRs), and Home Location Registers (HLRs) having Authentication Centers (ACs or AuCs). Each base station provides radio communications to mobile terminals located in a respective cell or zone of the wireless network. The base stations are interconnected by the MSCs which provide telecommunications switching functions. The HLR stores information related to the current location of each mobile terminal and subscriber data which define the authorized services for each mobile terminal. The VLR temporarily stores subscriber data for those mobile terminals currently located in the service area of the corresponding MSC.
When a mobile terminal is activated in a zone of the wireless network, it sends a registration request to the base station serving the zone in which it is located. The registration request includes a Mobile Identification Number (MIN), which uniquely identifies the mobile terminal. The serving base station forwards the registration request to the serving MSC, which then forwards the registration request to the HLR. The HLR searches for subscriber data corresponding to the MIN in the registration request. If the subscriber data is located, the HLR downloads that data to the VLR of the serving MSC. The serving MSC then uses the subscriber data to perform any required authentication tests and, upon finding such tests satisfied, provides the services defined by the subscriber data to the mobile terminal.
Wireless networks are connected to other wireless networks, and support mobile terminals that roam into their service areas from the service areas of other wireless networks. Subscriber data for the roaming mobile terminals is downloaded from the HLRs of their home networks to the VLR in the serving network. In North American cellular telephone systems, roaming mobile terminals send enough information to the serving MSC in the registration request to enable the serving MSC to locate and establish communications with the HLR of the mobile terminal's home network. This allows the required subscriber data to be downloaded to the VLR in the serving network.
The IS-41 standard defines the protocol North American cellular telephone systems use to locate the home HLR of a registering mobile terminal to download subscriber data for the registering terminal from the home HLR to the VLR of the serving MSC, and to authenticate the registering terminal. North American cellular, up-banded cellular, and CDMA wireless telephone systems use this protocol.
The Global System for Mobile Communication (GSM) series of standards defines a different protocol used for the same operations in most European cellular telephone systems. The PCS-1900 standard for personal communications services (PCS) in North America is based on the GSM standard.
In North America, some PCS service providers (PSPs) use the IS-41 mobility management protocol and other PSPs use the GSM mobility management protocol. To earn revenue from those subscribers who roam over large geographic regions, PSPs need to support GSM-based PCS subscribers on IS-41-based networks and IS-41-based subscribers on GSM-based networks in order to provide those subscribers with unbroken service.
To support such roaming of mobile terminals between cellular telephone systems using different mobility management protocols, conventional systems include an interworking function. The interworking function receives registration requests formatted according to the mobility management protocol used by the serving system and provides corresponding subscriber data in a format used by the VLRs and MSCs of the serving system.
One prior art technique for supporting mobile terminal roaming is discussed in an article by Jorgen Lantto, "Roaming Between Cellular Standards," ISS'95, Vol. 1, April 1995. This technique, referred to as the Ericsson technique, is demonstrated in FIGS. 1-3 for the case where a GSM terminal roams into an IS-41 service area.
As FIG. 1 shows, the Ericsson technique uses an Interworking Location Register (ILR) and an Interworking MSC (IMSC) or Gateway MSC (GMSC) to perform the required interworking functions. The ILR is a normal HLR and acts as an IS-41 HLR towards the serving IS-41 network and as a GSM MSC/VLR towards the home GSM network. The ILR contains the normal functions of an IS-41 HLR, but includes only subscriber data for roaming terminals.
FIG. 2 demonstrates the registration procedure, and FIG. 3 demonstrates the call termination procedure of the Ericsson technique. When the roaming mobile terminal realizes that it is no longer located within its home GSM network, the registration procedure of FIG. 2 occurs. The roaming terminal requests registration from the serving network via a registration request (RegReq) message (210). The serving MSC/VLR sends the registration request (RegReq) message to the ILR (220).
Upon receiving the RegReq message, the ILR authenticates the roaming terminal and stores the identification of the serving MSC/VLR (230). The ILR sends subscriber data identifying the roaming terminal to the serving MSC/VLR in the form of a registration request response (regreq) message (240). Finally, the ILR updates the home HLR to identify the IMSC as the serving MSC for the roaming terminal (250).
When an incoming call arrives at the network for the roaming terminal, it first arrives at the roaming terminal's home MSC/VLR (310). In response to the received call for the roaming terminal, the home MSC/VLR determines whether the terminal is located within its serving area. Since the terminal is roaming, the home MSC/VLR determines that the terminal is not located within its serving area.
The home MSC/VLR then requests a routing number from the home HLR by sending a routing number request (ReqRouteNo) message. The home MSC/VLR uses the routing number to route the call to the appropriate serving MSC.
The home HLR forwards the routing number request to the ILR (330), which forwards the request to the IMSC (340). The IMSC provides a routing number (RouteNo) to the ILR identifying itself as the serving MSC (350). The ILR forwards the routing number to the home MSC/VLR via the home HLR (360-370). Using this routing number, the home MSC/VLR forwards the call to the IMSC via a Public Switched Telephone Network (PSTN) (380).
Upon receiving the forwarded call, the IMSC requests a routing number from the ILR for forwarding the call to the serving system (390). The ILR transmits the request to the serving MSC/VLR (3100). The serving MSC/VLR provides a routing number in a routing number response (routeno) message to the ILR, identifying itself as the serving MSC (3110). The ILR forwards the routing number to the IMSC (3120).
Using this routing number, the IMSC forwards the call to the serving MSC/VLR via the PSTN (3130). Upon receiving the call, the serving MSC/VLR routes the call to the roaming terminal via its base station (3140).
The Ericsson technique has several disadvantages. First, certain subscriber data must be duplicated at the ILR. This not only consumes storage space, but also complicates data integrity requirements and increases messaging requirements because all copies of the subscriber data are updated simultaneously. Second, the ILR and the IMSC must be shared and operated in cooperation by the two PSPs of the interworking systems. This causes problems when the PSPs have conflicting interests. Third, the cost of providing an extra MSC dedicated to interworking, namely the IMSC, is high. Finally, routing calls through the IMSC consumes more PSTN resources and is relatively slow.